In the liquid crystalline transfer sheet as described above, a release layer or easily separable adhesive layer has conventionally been provided between the liquid crystal layer and the substrate so that the liquid crystal layer can easily be separated from the substrate, thereby making it possible to successfully transfer the liquid crystal layer to a receiving object.
To transfer the liquid crystal layer to a receiving object, it is necessary to stick the liquid crystal layer to the receiving object. Having been commonly employed for this purpose is such a conventional means that an adhesive layer is provided between the liquid crystal layer and a receiving object to which the liquid crystal layer is transferred. Specifically, an adhesive layer is provided in advance either on the transfer-side surface of the liquid crystal layer (surface to be adhered to a receiving object) or on a receiving object. Alternatively, an adhesive layer is formed on the transfer-side surface of the liquid crystal layer or on a receiving object in the process of transferring the liquid crystal layer to the receiving object.
Another means for sticking the liquid crystal layer to a receiving object is thermocompression bonding.
The above-described liquid crystalline transfer sheet containing a release layer or easily separable adhesive layer provided between the liquid crystal layer and the substrate is to have an increased number of layers, so that it has complicated constitution of lamination. Moreover, the substances constituting the release layer or easily separable adhesive layer can mingle with the liquid crystal layer or can partially stick to the liquid crystal layer when the liquid crystal layer is separated; the liquid crystal layer that has been transferred to a receiving object can thus show lowered optical properties.
Of the aforementioned liquid crystalline transfer sheets, a liquid crystalline transfer sheet of the type which the liquid crystal layer is adhered to a receiving object through an adhesive layer is disadvantageous in that the liquid crystal layer transferred to the receiving object shows lowered optical properties because of the adhesive layer provided. One cause of this lowering of the optical properties is interfacial reflection that occurs at the interface of the adhesive layer and the liquid crystal layer as well as at the interface of the adhesive layer and the receiving object. Another cause is as follows: the adhesive layer changes its shape because of its fluidity when transferred to a highly even receiving object, so that the thickness of the adhesive layer becomes non-uniform; as a result, the liquid crystal layer adhered to the receiving object through such an adhesive layer is to have decreased evenness.
Further, it is not easy to make an adhesive layer thin (1 μm or less), so that it inevitably has a thickness to some extent. Many adhesive layers are therefore colored, or cause separation, or yellow, when heated as disclosed in Japanese Laid-Open Patent Publications No. 313729/1996, No. 29325/1999, No. 75924/1996, No. 151877/1999, etc. In particular, adhesive layers made from acrylic resins, as disclosed in Japanese Laid-Open Patent Publication No. 28827/2000, are known to yellow at high temperatures of more than 200° C.
Of the above-described liquid crystalline transfer sheets, a liquid crystalline transfer sheet of the type which the liquid crystal layer is adhered to a receiving object via thermocompression bonding is also disadvantageous in that it is not easy to peel the substrate from the liquid crystal layer after the liquid crystal layer formed on the substrate has been adhered to a receiving object via thermocompression bonding, if the release layer, easily separable adhesive layer or adhesive layer as described above is not provided.
The above-described phenomenon depends on materials for the substrate and the receiving object, and occurs when the adhesion between the liquid crystal layer to be transferred and the substrate is stronger than the adhesion between the liquid crystal layer and the receiving object. In such a case, it is not easy to peel the substrate from the liquid crystal layer after the liquid crystal layer has been adhered to the receiving object. In particular, if the liquid crystal layer is extremely thin, it can be broken when the substrate is tried to peel from the liquid crystal layer. In addition, as disclosed in Japanese Laid-Open Patent Publication No. 311710/1999, for example, there is such a case where a cholesteric liquid crystal layer is adhered to another cholesteric liquid crystal layer via thermocompression bonding. Even in this case, if the cholesteric liquid crystal layers are thin or the adhesion between the cholesteric liquid crystal layer and the substrate is stronger than that between the cholesteric liquid crystal layers, it is difficult to transfer the cholesteric liquid crystal layers to a receiving object, and the cholesteric liquid crystal layers can be damaged (broken).